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Microvascular dysfunction due to hypoxia is a key contributor in the pathogenesis of many disorders including cancer and retinal and cardiovascular diseases, but relevant human models are missing. Here, we present a robust 3D in vitro method with the use of human induced pluripotent stem cell–derived blood vessel organoids to analyze in vitro microvascular remodeling. We present a detailed practical pipeline combining optical tissue clearing, high-resolution immunofluorescence, and surface marker analysis to quantitatively assess hypoxia-driven changes in endothelial cells, pericytes, and the basal lamina. Exposure of these blood vessel organoids to chronic hypoxia (1% O2) for 1 week recapitulated key pathological features, including structural remodeling and a dysregulated secretome with altered vascular endothelial growth factor signaling. This approach establishes a versatile and human-relevant platform to study microvascular remodeling induced by chronic hypoxia and other pathological stimuli and their contribution to microvascular-related diseases.

Parvovirus B19 (B19V) is a prevalent human pathogen that can cross the placenta by a mechanism that remains unknown, posing a risk of severe fetal complications, particularly during the first trimester of pregnancy. We investigated the expression of B19V-specific receptors in the three trophoblast cell types, cytotrophoblasts (CTBs), syncytiotrophoblasts (STBs), and extravillous trophoblasts (EVTs), and assessed their susceptibility to infection. VP1uR, the receptor that mediates viral uptake and infection in erythroid progenitor cells, is expressed in CTBs and STBs, but not in EVTs. Globoside, a glycosphingolipid that is essential for the escape of the virus from endosomes, is also expressed in these cells, except for choriocarcinoma-derived CTBs. In the latter, the absence of globoside can be overcome by promoting endosomal leakage with polyethyleneimine. While erythropoietin receptor (EpoR) signaling is associated with the strict erythroid tropism of B19V, it is not required for infection in trophoblasts. Transfection experiments revealed that highly proliferative first-trimester CTBs are more susceptible to B19V infection than the low-proliferative CTBs from term placenta. These findings demonstrate that B19V targets specific trophoblast cells, where viral entry and replication are collectively mediated by VP1uR, globoside, and high cellular proliferative activity, but are independent of EpoR signaling. Author summaryParvovirus B19 is a common human pathogen that can cross the placenta and infect the fetus, though the mechanism remains unknown. Here, we demonstrate that specific trophoblast populations at the maternal-fetal interface create conditions that enable infection. Viral entry and replication depend on specific receptors expressed in the syncytiotrophoblasts and cytotrophoblasts in placental villi, as well as the high proliferative activity that is characteristic of the early stages of gestation. Unlike erythroid progenitor cells, trophoblast infection occurs independently of erythropoietin signaling. These findings broaden the known erythroid tropism of B19V to include trophoblast cells, providing a mechanistic explanation for the heightened vulnerability of the early placenta to B19V.

Aging is one of the most prominent risk factors for neurodegeneration, yet the molecular mechanisms underlying the deterioration of old neurons are mostly unknown. To efficiently study neurodegeneration in the context of aging, we transdifferentiated primary human fibroblasts from aged healthy donors directly into neurons, which retained their aging hallmarks, and we verified key findings in aged human and mouse brain tissue. Here we show that aged neurons are broadly depleted of RNA-binding proteins, especially spliceosome components. Intriguingly, splicing proteins—like the dementia- and ALS-associated protein TDP-43—mislocalize to the cytoplasm in aged neurons, which leads to widespread alternative splicing. Cytoplasmic spliceosome components are typically recruited to stress granules, but aged neurons suffer from chronic cellular stress that prevents this sequestration. We link chronic stress to the malfunctioning ubiquitylation machinery, poor HSP90? chaperone activity and the failure to respond to new stress events. Together, our data demonstrate that aging-linked deterioration of RNA biology is a key driver of poor resiliency in aged neurons. Rhine et al. find that neuronal aging leads to widespread dysregulation of RNA biology, including mislocalization of splicing proteins like TDP-43, chronic cellular stress and reduced resiliency.